1. Field of the Invention
The detection of the presence of a material and/or its amount in a particular environment becomes increasingly important in a society which seeks to monitor and manipulate its environment. Despite the long history of developing devices for measurement of various materials in liquid media, there still remain ample opportunities for improvements in sensitivity, efficiency, economy, and ease of use. Among the manifold detection methods, one device which has found recent application is the field effect transistor (FET) and various modifications of the device. Various studies have been directed to the use of FETs for measurement of organic molecules. See for example, Stenberg et al., J. Coll. Interface and Sci. (1979) 72:255-264; Bergveld and DeRooij, Med Biol. Eng. Compt. (1979) 17:647-654; Bergveld et al., IEEE Trans. BMI-23 (1976) pages 136-144; and Lauks and Zemel; IEEE Trans. on Electron Devices, Vol. ED-26, No. 12 (December 1979), pages 10959-10964. These references are merely illustrative of references directed to semiconductor device, particularly field effect transistors, for measurement of material in solution. The FET devices have not found commercial acceptance and in many sitations, lack flexibility. For use as chemical detectors, FET devices particularly suffer from the difficulty of obtaining exposed gate regions and working with them in an experimental environment.
As compared to other devices, semiconductive or other devices which respond to an electrical signal provide for a number of advantages. The electrically responsive device can respond to relatively small signals. Furthermore, by various techniques, the signal can be modulated and the background noise diminished or substantially eliminated. Electrical devices can frequently be miniaturized, so that relatively small equipment can be developed for measurement of changes in various fluids.
2. Description of the Prior Art
References of interest include Gronet and Lewis, Nature (1982) 300:733-735; Bard and Faulkner, 1980. Electrochemical Methods--Fundamentals and Applications, John Wiley and Sons, New York; Fahrenbruch and Bube, 1983. Fundamentals of Solar Cells--Photovoltaic Energy Conversion, Academic Press, New York; Fonash, 1981; Solar Cell Device Physics, Academic Press, New York; and Photoeffects at Semiconductor-Electrolyte Surfaces, ed. Nozik, American Chemical Society, Washington, D.C., 1981. See also U.S. Pat. No. 4,293,310 and PCT Application No. WO83/02669. Of particular interest to the measurement of solution pH with a semiconductor electrode is Y. G. Vlasov, A. J. Bratov, and V. P. Letavin, In: Ion-Selective Electrodes 3, Analytical Chemistry Symposium Series Vol. 8 (E. Pungor, Ed.) Elsevier Publ. Co., Amsterdam, 1981; Luc Bousse, Thesis, Twente University, The Netherlands, 1982; M. T. Pham and W. Hoffman, Sensors and Actuators (1984) 5:217-228; F. Chauvet and A. Amari, Sensors and Actuators (1984) 6:255-267; whose disclosures are incorporated herein by reference.